1991 ACURA NSX air conditioning

Cylinder Head/Valve Train
Illustrated Index

CAUTION: To avoid damaging the cylinder head, wait

until the engine coolant temperature drops below
100 °F (38 °C) before removing it.NOTE:

CAP NUT

6 x 1.0 mm
10 N .
m
(1.0 kg-m,

7 Ib-ft)
CYLINDER

HEAD COVER

WASHER AND

GROMMET

After installation, fill the engine with oil up to the

specified level, run the engine for more than 3

minutes, then check for oil leakage.

When installing the new crankshaft;

tighten the crankshaft pulley bolt to 280 N .
m (28

kg-m, 203 Ib-ft),

loosen bolt.


retighten it to

250 N .
m (25 kg-m, 181 Ib-ft).

CYLINDER HEAD

COVER
RUBBER SEALS
Replace when damaged

or deteriorated.

6 x 1.0 mm
12N .
m (1.2 kg-m,

9 Ib-ft)

TIMING BELT
REAR MIDDLE

COVER

TIMING BELT
FRONT MIDDLE

COVER
ADJUSTING BOLT

10 x
1.25
mm

43N .
m (4.3 kg-m,

31 Ib-ft)

For adjustment only,
do not remove.

ALTERNATOR

BELT

Adjustment,
section 23

6 x 1.0 mm
12N .
m
(12
kg-m.

9 Ib-ft)

CRANKSHAFT PULLEY
Remove any oil.

SPECIAL BOLT
16x 1.5 mm

250N .
m (25 kg-m,

181 Ib-ft

Tightening torque for
a new crankshaft.

203

Apply oil to
the bolt threads, but not
to the surface that contacts the washer.
6 x 1.0 mm

12N .
m (1.2 kg-m,

9 Ib-ft)
AIR CONDITIONING (A/C) BELT
Adjustment, section 22
6x 1.0 mm

12N .
m (1.2 kg-m, 9 Ib-ft)

(cont'd)

A/C ADJUSTING

PULLEY BRACKET

RUBBER SEAL
Install with concave

surface facing out.

Remove any oil.
TIMING BELT

DRIVE PULLEY

Remove any oil.

Install with concave
surface facing in.
Remove any oil.

TIMING BELT

Inspection, page 6-22
Adjustment, page 6-22 Replacement, page 6-23 to 26
RUBBER SEALS

Replace when damaged
or deteriorated.
CAP NUT

6 x 1.0 mm

10N .
m (1.0 kg-m,

7 Ib-ft)

TIMING BELT

LOWER COVER

RUBBER SEAL
KEY

Remove any oil.

TENSIONER

280

250N.m

25
kg-m,
181 Ib-ft)

(28
0
0
0

Use new O-rings and gaskets when reassembling.

Replace rubber seals, if damaged or deteriorated.

Prior to installing the cylinder head cover, apply a thin

layer of liquid gasket to the mating surface of the

cylinder head cover and rubber seals to prevent the
rubber seal from falling off.ProCarManuals.com

45N
.
m (4.5 kg-m. 33 Ib-ft)

14. Remove the connector, the terminal and the alternator.
1 5. Remove the bolt from the side engine mount, then
push the side mounting bracket into the housing of
the body (page 5-27).
16. Remove the transmission mount.
17. Remove the cylinder head covers.

18. Turn the crankshaft so that the No. 1 piston is at

top dead center (page 6-25, 26).

19.
Install
a
brace
under
the
engine, then
tilt
the
engine approximately 5° using a jack.
Timing Belt
Removal (cont'd)
BELT COVER
ALTERNATOR
20. Remove the alternator bracket stiffener.
ALTERNATOR BRACKET
STIFFENER

21. Remove the air conditioning (A/C) compressor ad-
justing pulley and belt.

22. Remove the dipstick pipe mounting bolt, then re- move the front and rear timing belt middle covers.
23. Remove the crankshaft pulley, then remove the tim- ing belt lower cover.
24. Loosen the timing belt adjusting bolt 180° and release the belt tension.
NOTE: Push the tensioner to release tension from
the belt, then retighten the adjusting bolt.
ADJUSTING BOLT
Do not remove. When

adjusting, loosen

it
180°.
25. Remove the timing belt from the pulleys.
CAUTION: Do not crimp or bend the timing belt more

than 90° or less than 25 mm (1 in.) in diameter.
DIAMETER

1.0 x
1.25
mm

45N .
m (4.5 kg-m,

33 Ib-ft)

6 x 1.0 mm

12N .
m (1.2 kg-m, 9 Ib-ft) DIPSTICK PIPE

8x1.25 mm

22N .
m

(2.2 kg-m,
16 Ib-ft)
9 Ib-ft)
6 x 1.0 mm

12N .
m (1.2 kg-m.

6 Ib-ft29

ADJUSTING BOLT

8x1.25 mm

8N .
m (0.8 kg-m,

1.0 x
1.25
mm
8x1.25 mm

12N .
m (1.2 kg-m,

9 Ib-ft)ProCarManuals.com

14. Relieve fuel pressure (see section 11).
Do not smoke while working on fuel
system; keep open flame or spark away from work
area. Drain fuel only into an approved container.
1 5. Disconnect the fuel feed pipe and the return hose
(page 5-21).

16. Remove the ignition coil covers, the wire harness covers, the ignition coils and the connectors (page
6-23).
17. Remove the water hoses, then remove the expan- sion tank (page 5-21).
18. Remove the breather hose, and the air cleaner housing (page 5-22).
19. Remove the brake booster hose, the evaporative emission (EVAP) control canister hose and other
hoses from the intake manifold and throttle body
(page 5-22).
20. Remove the emission control box (page 5-23). Do not disconnect emission hose.Disconnect the three connectors before
removing.
21. Remove the connector, the terminal and the alternator.
22. Disconnect the following engine wire harness con- nectors, then remove the harness clamps from thecylinder head and the intake manifold.
Front cylinder head:

Crankshaft position (CKP)/cylinder position
(CYP) sensor connector
Air conditioning (A/C) compressor magnetic clutch connector
Heated oxygen sensor (H02S) connector
Ground cable terminals Three injector connectors (cylinders No. 4, 5

and 6)

Intake air temperature (IAT) sensor connector
Ignition control module (ICM) connector
Condenser connector

Engine oil pressure gauge sending unit

connector

VTEC solenoid valve connector
VTEC pressure switch connector
Engine coolant temperature (ECT) sensor

connector
ECT sending unit connector
Accelerator pedal opening sensor connector

(throttle body)

Radiator fan control sensor connector
Rear cylinder head: Engine oil pressure switch connector (oil cooler

base)

Heated oxygen sensor connector
Three injector connectors (cylinders No. 1, 2

and 3)
Idle air control (IAC) valve connector
Knock sensor connector
Throttle actuator motor connector

Throttle position sensor connector

VTEC solenoid valve connectorVTEC pressure switch connector
ICM connector

Ground terminal

ICM CONNECTORS THROTTLE ACTUATOR

MOTOR CONNECTOR

THROTTLE POSITION
SENSOR CONNECTOR
ACCELERATOR PEDAL OPENING
SENSOR CONNECTORProCarManuals.com

PGM-FI System

System Description

INPUTS
ENGINE CONTROL MODULE (ECM)

OUTPUTS

FRONT HO2S

REAR HO2S

MAP Sensor

CKP/CYP Sensor

ECT Sensor

TP Sensor

IAT Sensor

VSS

FRONT KS

REAR KS

Ignition Timing Adjuster

EGR Valve Lift Sensor

A/T Fl Signals

TCS Signals

Starter Signal

ALT FR Signal

Air Conditioning Signal

A/T Gear Position Switch Signal

Neutral Switch Signal (M/T)

Clutch Switch Signal (M/T)

VTEC Pressure Switch

Battery Voltage (IGN.1)

Fuel Pump Terminal Voltage
Fuel Injectors

PGM-FI Main Relay (Fuel Pump)

Malfunction Indicator Lamp

IAC Valve

A/C Compressor Clutch Relay

ICM

EVAP Purge Control Solenoid Valve

Fuel Pump Relay

EGR Control Solenoid Valve

IAB Control Solenoid Valve

Engine Compartment Fan Relay

VTEC Solenoid Valve

TCS Control Signals

FRONT HO2S HEATER

REAR HO2S HEATER

PGM-FI System

The PGM-FI system on this model is a sequential multiport fuel injection system.

Fuel Injector Timing and Duration

The ECM contains memories for the basic discharge durations at various engine speeds and manifold pressures. The

basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors

to obtain the final discharge duration.

Idle Air Control

Idle Air Control (IAC) Valve

When the engine is cold, the A/C compressor is on, the transmission is in gear (A/T only) or the alternator (ALT) is charg-

ing, the ECM controls current to the IAC valve to maintain correct idle speed.

Ignition Timing Control

The ECM contains memories for basic ignition timing at various engine speeds and manifold pressures. Ignition timing

is also adjusted for engine coolant temperature.

A knock control system is also used. When detonation is detected by the knock sensor (KS), the ignition timing is

retarded.

Other Control Functions

1. Starting Control

When the engine is started, the ECM provides a rich mixture by increasing fuel injector duration.

2. Fuel Pump Control

When the ignition switch is initially turned on, the ECM supplies ground to the PGM-FI main relay that supplies

current to the fuel pump for two seconds to pressurize the fuel system.

When the engine is running, the ECM supplies ground to the PGM-FI main relay that supplies current to the fuel pump.

When the engine is not running and the ignition is on, the ECM cuts ground to the PGM-FI main relay which cuts

current to the fuel pump.

Excellent engine performance is achieved through the use of VTEC (Variable Valve Timing and Valve Lift Electron-

ic Control System), intake air bypass control and discharge volume control of the fuel pump.ProCarManuals.com

3. Fuel Cut-off Control

During deceleration with the throttle valve closed, current to the fuel injectors is cut off to improve fuel economy

at speeds over 1,500 rpm.

Fuel cut-off action also takes place when engine speed exceeds, 8,300 rpm, regardless of the position of the

throttle valve, to protect the engine from over-revving.

4. A/C Compressor Clutch Relay

When the ECM receives a demand for cooling from the air conditioning system, it delays the compressor from being

energized, and enriches the mixture to assure smooth translation to the A/C mode.

5. Evaporative Emission (EVAP) Purge Control Solenoid Valve

When the engine coolant temperature is below 1 58 °F (70°C) the ECM supplies a ground to the EVAP purge control

solenoid valve which cuts vacuum to the EVAP purge control diaphragm valve.

6. Intake Air Bypass (IAB) Control Solenoid Valve

When the engine speed is below 4,800 rpm, the IAB control solenoid valve is activated by a signal from the ECM.

Intake air then flows through the smaller chamber, and hight torque is delivered. To increase air flow at engine speeds

higher than 4,800 rpm, the solenoid valve is deactivated by the ECM, and the intake air flows through the larger

chamber.

7. Exhaust Gas Recirculation (EGR) Control Solenoid Valve

When the EGR is required for control of oxides of nitrogen (NOx) emissions, the ECM supplies ground to the EGR

control solenoid valve which supplies regulated vacuum to the EGR valve.

ECM fail-safe/back-up Functions

1. Fail-Safe Function

When an abnormality occurs in a signal from a sensor, the ECM ignores that signal and assumes a pre-programmed

valve for that sensor that allows the engine to continue to run.

2. Back-up Function

When an abnormality occurs in the ECM itself, the fuel injectors are controlled by a back-up circuit independent of

the system in order to permit minimal driving.

3. Self-diagnosis Function [Malfunction Indicator Lamp (MIL)]

When an abnormality occurs in a signal from a sensor, the ECM lights the MIL and stores the diagnostic trouble code

in erasable memory. When the ignition is initially turned in, the ECM supplies ground for the MIL for two seconds

to check the MIL bulb condition.ProCarManuals.com

1. When the idle speed is out of specification and the Malfunction Indicator Lamp (MIL) does not blink code 14, check

the following items:
Adjust the idle speed (see page 11-102)
Air conditioning signal (see page 11 -90)
ALT FR signal (see page 11-92)
A/T gear position switch signal (see page 11-94)Neutral switch signal (M/T) (see page 11-96)
Clutch switch signal (M/T) (see page 11-98)
Starter switch signal (see page 11-100)Fast idle thermo valve (see page 11-101)
Hoses and connections
IAC valve and its mounting O-rings
2. If the above items are normal, substitute a known-good IAC valve and readjust the idle speed (see page 11-102). If the idle speed still cannot be adjusted to specification (and the MIL does not blink code 14) after IAC valve
replacement, substitute a known-good ECM and recheck. If symptom goes away, replace the original ECM.ProCarManuals.com

Idle Control System

Troubleshooting Flowchart
Air Conditioning Signal

This signals the ECM when there is a demand for cooling from the air conditioning system.

Inspection of Air Condition-

ing Signal.
Connect the test harness be-
tween the ECM and connector. Disconnect "C" connector from
the engine wire harness only, not
the ECM (see page 11-37).
Turn the ignition switch ON.
Measure voltage between C3 (+)

terminal and A26 (-) terminal.

Is there approx. 10 V?

Turn the ignition switch OFF.
Reconnect "C" connector to the
engine wire harness.

Turn the ignition switch ON.

Momentarily connect A15 ter-
minal to A26 terminal several

times.

Is there a clicking noise from the
A/C compressor clutch?

Start the engine.

Blower switch ON.
(To page 11-91) Repair open in RED/BLU wire be-
tween ECM (A15) and A/C
clutch relay. Is there a clicking noise from the
A/C compressor clutch?
Connect the RED/BLU terminal of
the 4P connector on the A/C
clutch relay to body ground. View from relay side
(sub relay box A)

RED/BLU

See air conditioner in-
spection (see section
22).
Substitute a known-
good ECM and re-
check. If prescribed
voltage is now avail-
able, replace the ori-
ginal ECM.ProCarManuals.com

(From page 11-90)
A/C switch ON.
Does A/C operate ?

Air conditioning signal is OK.
Is voltage less than 1.0 V?
Measure voltage between C3

( + ) terminal and A26 (-) ter-

minal.

Substitute a known-good ECM
and recheck. If symptom/indica-
tion goes away, replace the orig- inal ECM. Repair open in BLU/
BLK wire between ECM
(C3) and A/C switch.ProCarManuals.com